Sichuan peppercorn is the ingredient that most distinguishes Sichuan cooking and is well worth buying in quantity in Chengdu, where fresh supplies come from the producing regions of Hanyuan and Jiangjin. The difference between freshly dried Sichuan pepper and the powdery, flavourless stuff sold overseas is profound.
The Jinli souvenir area sells small decorative packages aimed at tourists, but the markets around the wholesale food district near the South Bus Station sell proper quantities at very cheap prices. Look for bright, orangey-red husks that have not fully opened — these are the freshest. Buy both whole and pre-ground. Also buy whole dried Sichuan chilies (erjingtiao variety) and good-quality Pixian doubanjiang if travelling home.